Has anyone seen this?

A small cylinder with a steel wire extending therefrom, the wire being
wound around an internal spool, the spool being spring loaded to
persuade
the wire to wind around the spool. The wire extends a foot or two.

I spotted an image and description of these on a site last week, the
price
was about 3-4 dollars, I have lost the doggone reference, so can't find
it again.

Why?

I thought it might be nifty to attach one of those Electronic Goldmine
rotary encoders to the shaft of the spool, attach the end of the wire to

my lathe carriage, and see what happened..... If it turns out that the
wire is wound in a single layer on the spool, then we have a cheap way
to get the DRO package up and running.....

I thought it might have been in the new H&R catalog I got, but I've been

thru it several times while sitting on the throne....

Any help / comment would be appreciated.
/mark